Makefile: use SVG externs when typechecking.
svg.Svg: correct a return type.
svg.Path+tests: move pathData out of ctor to allow setting after construction.
svg.{ElementHandler,Svg}: add some preliminary methods for matrix stuff.
demo: add a demo of a Bezier curve following the mouse.
update JsDoc comments.
svg.ElementHandler: make a method protected.
introduce a PathComponent interface to help refactor PathData.
svg.PathData: manage svg.PathComponents instead of raw strings.